Patchwork [v4,3/3] Inter-VM shared memory PCI device

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Submitter Cam Macdonell
Date April 7, 2010, 10:52 p.m.
Message ID <1270680720-8457-4-git-send-email-cam@cs.ualberta.ca>
Download mbox | patch
Permalink /patch/49673/
State New
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Comments

Cam Macdonell - April 7, 2010, 10:52 p.m.
Support an inter-vm shared memory device that maps a shared-memory object as a
PCI device in the guest.  This patch also supports interrupts between guest by
communicating over a unix domain socket.  This patch applies to the qemu-kvm
repository.

    -device ivshmem,size=<size in MB>[,shm=<shm name>]

Interrupts are supported between multiple VMs by using a shared memory server
by using a chardev socket.

    -device ivshmem,size=<size in MB>[,shm=<shm name>][,chardev=<id>][,msi=on]
            [,irqfd=on][,vectors=n]
    -chardev socket,path=<path>,id=<id>

Sample programs, init scripts and the shared memory server are available in a
git repo here:

    www.gitorious.org/nahanni
---
 Makefile.target |    3 +
 hw/ivshmem.c    |  700 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 qemu-char.c     |    6 +
 qemu-char.h     |    3 +
 4 files changed, 712 insertions(+), 0 deletions(-)
 create mode 100644 hw/ivshmem.c
Avi Kivity - April 12, 2010, 8:56 p.m.
On 04/08/2010 01:52 AM, Cam Macdonell wrote:
> Support an inter-vm shared memory device that maps a shared-memory object as a
> PCI device in the guest.  This patch also supports interrupts between guest by
> communicating over a unix domain socket.  This patch applies to the qemu-kvm
> repository.
>
>      -device ivshmem,size=<size in MB>[,shm=<shm name>]
>    

Can that be <size in format accepted by -m> (2M, 4G, 19T, ...).

> Interrupts are supported between multiple VMs by using a shared memory server
> by using a chardev socket.
>
>      -device ivshmem,size=<size in MB>[,shm=<shm name>][,chardev=<id>][,msi=on]
>              [,irqfd=on][,vectors=n]
>      -chardev socket,path=<path>,id=<id>
>    

Do we need the irqfd parameter?  Should be on by default.

On the other hand, it may fail with older kernels with limited irqfd 
slots, so better keep it there.

> Sample programs, init scripts and the shared memory server are available in a
> git repo here:
>
>      www.gitorious.org/nahanni
>    

Please consider qemu.git/contrib.

> ---
>   Makefile.target |    3 +
>   hw/ivshmem.c    |  700 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>   qemu-char.c     |    6 +
>   qemu-char.h     |    3 +
>    

qemu-doc.texi | 45 +++++++++++++

>   4 files changed, 712 insertions(+), 0 deletions(-)
>   create mode 100644 hw/ivshmem.c
>
> diff --git a/Makefile.target b/Makefile.target
> index 1ffd802..bc9a681 100644
> --- a/Makefile.target
> +++ b/Makefile.target
> @@ -199,6 +199,9 @@ obj-$(CONFIG_USB_OHCI) += usb-ohci.o
>   obj-y += rtl8139.o
>   obj-y += e1000.o
>
> +# Inter-VM PCI shared memory
> +obj-y += ivshmem.o
> +
>    

depends on CONFIG_PCI

>   # Hardware support
> +
> +#define PCI_COMMAND_IOACCESS                0x0001
> +#define PCI_COMMAND_MEMACCESS               0x0002
>    

Should be in pci.h?

> +
> +#define DEBUG_IVSHMEM
>    

Disable for production.

> +
> +#define IVSHMEM_IRQFD   0
> +#define IVSHMEM_MSI     1
> +#define IVSHMEM_MAX_EVENTFDS  16
>    

Too low?  why limit?
> +
> +struct eventfd_entry {
> +    PCIDevice *pdev;
> +    int vector;
> +};
>    

Coding style:  EventfdEntry, and a typedef.

> +
> +typedef struct IVShmemState {
> +    PCIDevice dev;
> +    uint32_t intrmask;
> +    uint32_t intrstatus;
> +    uint32_t doorbell;
> +
> +    CharDriverState * chr;
> +    CharDriverState ** eventfd_chr;
> +    int ivshmem_mmio_io_addr;
> +
> +    pcibus_t mmio_addr;
> +    uint8_t *ivshmem_ptr;
> +    unsigned long ivshmem_offset;
>    

off_t

> +    unsigned int ivshmem_size;
>    

ram_addr_t

> +
> +/* accessing registers - based on rtl8139 */
> +static void ivshmem_update_irq(IVShmemState *s, int val)
> +{
> +    int isr;
> +    isr = (s->intrstatus&  s->intrmask)&  0xffffffff;
>    

This is highly undocumented, but fits my suggested 'status is bitmap'.  
'isr' needs to be uint32_t if you mask it like that.

> +
> +    /* don't print ISR resets */
> +    if (isr) {
> +        IVSHMEM_DPRINTF("Set IRQ to %d (%04x %04x)\n",
> +           isr ? 1 : 0, s->intrstatus, s->intrmask);
> +    }
> +
> +    qemu_set_irq(s->dev.irq[0], (isr != 0));
> +}
> +
> +
>
>
> +
> +static void create_shared_memory_BAR(IVShmemState *s, int fd) {
> +
> +    s->shm_fd = fd;
> +
> +    s->ivshmem_offset = qemu_ram_mmap(s->shm_fd, s->ivshmem_size,
> +             MAP_SHARED, 0);
>    

Where did the offset go?

> +
> +    s->ivshmem_ptr = qemu_get_ram_ptr(s->ivshmem_offset);
>    

Never used, please drop.

> +
> +    /* region for shared memory */
> +    pci_register_bar(&s->dev, 2, s->ivshmem_size,
> +                       PCI_BASE_ADDRESS_SPACE_MEMORY, ivshmem_map);
>    

Might be worthwhile to mark it as a 64-bit BAR.  Please test with 
ridiculous shared memory sizes.

> +}
> +
> +static int ivshmem_irqfd(PCIDevice* pdev, uint16_t vector, int fd)
> +{
> +    struct kvm_irqfd call = { };
> +    int r;
> +
> +    IVSHMEM_DPRINTF("inside irqfd\n");
> +    if (vector>= pdev->msix_entries_nr)
> +        return -EINVAL;
> +    call.fd = fd;
> +    call.gsi = pdev->msix_irq_entries[vector].gsi;
> +    r = kvm_vm_ioctl(kvm_state, KVM_IRQFD,&call);
> +    if (r<  0) {
> +        IVSHMEM_DPRINTF("allocating irqfd failed %d\n", r);
> +        return r;
> +    }
> +    return 0;
> +}
>    

should be in kvm.c for reuse.

> +
> +static int ivshmem_ioeventfd(IVShmemState* s, int posn, int fd, int vector)
> +{
> +
> +    int ret;
> +    struct kvm_ioeventfd iofd;
> +
> +    iofd.datamatch = (posn<<  16) | vector;
> +    iofd.addr = s->mmio_addr + Doorbell;
> +    iofd.len = 4;
> +    iofd.flags = KVM_IOEVENTFD_FLAG_DATAMATCH;
> +    iofd.fd = fd;
> +
> +    ret = kvm_vm_ioctl(kvm_state, KVM_IOEVENTFD,&iofd);
>    

Ditto.

> +
> +    if (ret<  0) {
> +        fprintf(stderr, "error assigning ioeventfd (%d)\n", ret);
> +        perror(strerror(ret));
> +    } else {
> +        IVSHMEM_DPRINTF("success assigning ioeventfd (%d:%d)\n", posn, vector);
> +    }
> +
> +    return ret;
> +}
>    

blank line here.
Cam Macdonell - April 14, 2010, 11:30 p.m.
On Mon, Apr 12, 2010 at 2:56 PM, Avi Kivity <avi@redhat.com> wrote:
> On 04/08/2010 01:52 AM, Cam Macdonell wrote:
>>
>> Support an inter-vm shared memory device that maps a shared-memory object
>> as a
>> PCI device in the guest.  This patch also supports interrupts between
>> guest by
>> communicating over a unix domain socket.  This patch applies to the
>> qemu-kvm
>> repository.
>>
>>     -device ivshmem,size=<size in MB>[,shm=<shm name>]
>>
>
> Can that be <size in format accepted by -m> (2M, 4G, 19T, ...).
>
>> Interrupts are supported between multiple VMs by using a shared memory
>> server
>> by using a chardev socket.
>>
>>     -device ivshmem,size=<size in MB>[,shm=<shm
>> name>][,chardev=<id>][,msi=on]
>>             [,irqfd=on][,vectors=n]
>>     -chardev socket,path=<path>,id=<id>
>>
>
> Do we need the irqfd parameter?  Should be on by default.
>
> On the other hand, it may fail with older kernels with limited irqfd slots,
> so better keep it there.
>
>> Sample programs, init scripts and the shared memory server are available
>> in a
>> git repo here:
>>
>>     www.gitorious.org/nahanni
>>
>
> Please consider qemu.git/contrib.

Should the compilation be tied into Qemu's regular build with a switch
(e.g. --enable-ivshmem-server)? Or should it be its own separate
build?

Cam

>
>> ---
>>  Makefile.target |    3 +
>>  hw/ivshmem.c    |  700
>> +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  qemu-char.c     |    6 +
>>  qemu-char.h     |    3 +
>>
>
> qemu-doc.texi | 45 +++++++++++++

Seems to be light on qdev devices.  I notice there is a section named
"Data Type Index" that "could be used for qdev device names and
options", but is currently empty.  Should I place documentation there
of device there or just add it to "3.3 Invocation"?

>
>>  4 files changed, 712 insertions(+), 0 deletions(-)
>>  create mode 100644 hw/ivshmem.c
>>
>> diff --git a/Makefile.target b/Makefile.target
>> index 1ffd802..bc9a681 100644
>> --- a/Makefile.target
>> +++ b/Makefile.target
>> @@ -199,6 +199,9 @@ obj-$(CONFIG_USB_OHCI) += usb-ohci.o
>>  obj-y += rtl8139.o
>>  obj-y += e1000.o
>>
>> +# Inter-VM PCI shared memory
>> +obj-y += ivshmem.o
>> +
>>
>
> depends on CONFIG_PCI

as in

obj-($CONFIG_PCI) += ivshmem.o


the variable CONFIG_PCI doesn't seem to be set during configuration.
I don't see any other PCI devices that depend on it.  Do we also want
to depend on CONFIG_KVM?

>> +static void create_shared_memory_BAR(IVShmemState *s, int fd) {
>> +
>> +    s->shm_fd = fd;
>> +
>> +    s->ivshmem_offset = qemu_ram_mmap(s->shm_fd, s->ivshmem_size,
>> +             MAP_SHARED, 0);
>>
>
> Where did the offset go?

0 is the offset.  I include the offset parameter in qemu_ram_mmap() to
make it flexible for other uses.  Are you suggesting to take an
optional offset as an argument to -device?

Cam
Avi Kivity - April 15, 2010, 8:33 a.m.
On 04/15/2010 02:30 AM, Cam Macdonell wrote:
>>
>>> Sample programs, init scripts and the shared memory server are available
>>> in a
>>> git repo here:
>>>
>>>      www.gitorious.org/nahanni
>>>
>>>        
>> Please consider qemu.git/contrib.
>>      
> Should the compilation be tied into Qemu's regular build with a switch
> (e.g. --enable-ivshmem-server)? Or should it be its own separate
> build?
>    

It can have its own makefile.
>>> ---
>>>   Makefile.target |    3 +
>>>   hw/ivshmem.c    |  700
>>> +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>>   qemu-char.c     |    6 +
>>>   qemu-char.h     |    3 +
>>>
>>>        
>> qemu-doc.texi | 45 +++++++++++++
>>      
> Seems to be light on qdev devices.  I notice there is a section named
> "Data Type Index" that "could be used for qdev device names and
> options", but is currently empty.  Should I place documentation there
> of device there or just add it to "3.3 Invocation"?
>    

I think those are in qemu-options.hx.  Just put it somewhere where it 
seems appropriate.

>    
>>      
>>>   4 files changed, 712 insertions(+), 0 deletions(-)
>>>   create mode 100644 hw/ivshmem.c
>>>
>>> diff --git a/Makefile.target b/Makefile.target
>>> index 1ffd802..bc9a681 100644
>>> --- a/Makefile.target
>>> +++ b/Makefile.target
>>> @@ -199,6 +199,9 @@ obj-$(CONFIG_USB_OHCI) += usb-ohci.o
>>>   obj-y += rtl8139.o
>>>   obj-y += e1000.o
>>>
>>> +# Inter-VM PCI shared memory
>>> +obj-y += ivshmem.o
>>> +
>>>
>>>        
>> depends on CONFIG_PCI
>>      
> as in
>
> obj-($CONFIG_PCI) += ivshmem.o
>
>
> the variable CONFIG_PCI doesn't seem to be set during configuration.
> I don't see any other PCI devices that depend on it.

My mistake, keep as is.

> Do we also want
> to depend on CONFIG_KVM?
>    

No real need.

>>> +static void create_shared_memory_BAR(IVShmemState *s, int fd) {
>>> +
>>> +    s->shm_fd = fd;
>>> +
>>> +    s->ivshmem_offset = qemu_ram_mmap(s->shm_fd, s->ivshmem_size,
>>> +             MAP_SHARED, 0);
>>>
>>>        
>> Where did the offset go?
>>      
> 0 is the offset.  I include the offset parameter in qemu_ram_mmap() to
> make it flexible for other uses.

Makes sense.

> Are you suggesting to take an
> optional offset as an argument to -device?
>    

No need.

Patch

diff --git a/Makefile.target b/Makefile.target
index 1ffd802..bc9a681 100644
--- a/Makefile.target
+++ b/Makefile.target
@@ -199,6 +199,9 @@  obj-$(CONFIG_USB_OHCI) += usb-ohci.o
 obj-y += rtl8139.o
 obj-y += e1000.o
 
+# Inter-VM PCI shared memory
+obj-y += ivshmem.o
+
 # Hardware support
 obj-i386-y = pckbd.o dma.o
 obj-i386-y += vga.o
diff --git a/hw/ivshmem.c b/hw/ivshmem.c
new file mode 100644
index 0000000..2ec6c2c
--- /dev/null
+++ b/hw/ivshmem.c
@@ -0,0 +1,700 @@ 
+/*
+ * Inter-VM Shared Memory PCI device.
+ *
+ * Author:
+ *      Cam Macdonell <cam@cs.ualberta.ca>
+ *
+ * Based On: cirrus_vga.c and rtl8139.c
+ *
+ * This code is licensed under the GNU GPL v2.
+ */
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/io.h>
+#include <sys/ioctl.h>
+#include <sys/eventfd.h>
+#include "hw.h"
+#include "console.h"
+#include "pc.h"
+#include "pci.h"
+#include "sysemu.h"
+
+#include "msix.h"
+#include "qemu-kvm.h"
+#include "libkvm.h"
+
+#include <sys/eventfd.h>
+#include <sys/mman.h>
+#include <sys/socket.h>
+#include <sys/ioctl.h>
+
+#define PCI_COMMAND_IOACCESS                0x0001
+#define PCI_COMMAND_MEMACCESS               0x0002
+
+#define DEBUG_IVSHMEM
+
+#define IVSHMEM_IRQFD   0
+#define IVSHMEM_MSI     1
+#define IVSHMEM_MAX_EVENTFDS  16
+
+#ifdef DEBUG_IVSHMEM
+#define IVSHMEM_DPRINTF(fmt, args...)        \
+    do {printf("IVSHMEM: " fmt, ##args); } while (0)
+#else
+#define IVSHMEM_DPRINTF(fmt, args...)
+#endif
+
+#define NEW_GUEST_VAL UINT_MAX
+
+struct eventfd_entry {
+    PCIDevice *pdev;
+    int vector;
+};
+
+typedef struct IVShmemState {
+    PCIDevice dev;
+    uint32_t intrmask;
+    uint32_t intrstatus;
+    uint32_t doorbell;
+
+    CharDriverState * chr;
+    CharDriverState ** eventfd_chr;
+    int ivshmem_mmio_io_addr;
+
+    pcibus_t mmio_addr;
+    uint8_t *ivshmem_ptr;
+    unsigned long ivshmem_offset;
+    unsigned int ivshmem_size;
+    int shm_fd; /* shared memory file descriptor */
+
+    /* array of eventfds for each guest */
+    int * eventfds[IVSHMEM_MAX_EVENTFDS];
+    /* keep track of # of eventfds for each guest*/
+    int * eventfds_posn_count;
+
+    int vm_id;
+    int num_eventfds;
+    uint32_t vectors;
+    uint32_t features;
+    struct eventfd_entry eventfd_table[IVSHMEM_MAX_EVENTFDS];
+
+    char * shmobj;
+    uint32_t size; /*size of shared memory in MB*/
+} IVShmemState;
+
+/* registers for the Inter-VM shared memory device */
+enum ivshmem_registers {
+    IntrMask = 0,
+    IntrStatus = 4,
+    IVPosition = 8,
+    Doorbell = 12,
+};
+
+static inline uint32_t ivshmem_has_feature(IVShmemState *ivs, int feature) {
+    return (ivs->features & (1 << feature));
+}
+
+static inline int is_power_of_two(int x) {
+    return (x & (x-1)) == 0;
+}
+
+static void ivshmem_map(PCIDevice *pci_dev, int region_num,
+                    pcibus_t addr, pcibus_t size, int type)
+{
+    IVShmemState *s = DO_UPCAST(IVShmemState, dev, pci_dev);
+
+    IVSHMEM_DPRINTF("addr = %u size = %u\n", (uint32_t)addr, (uint32_t)size);
+    cpu_register_physical_memory(addr, s->ivshmem_size, s->ivshmem_offset);
+
+}
+
+/* accessing registers - based on rtl8139 */
+static void ivshmem_update_irq(IVShmemState *s, int val)
+{
+    int isr;
+    isr = (s->intrstatus & s->intrmask) & 0xffffffff;
+
+    /* don't print ISR resets */
+    if (isr) {
+        IVSHMEM_DPRINTF("Set IRQ to %d (%04x %04x)\n",
+           isr ? 1 : 0, s->intrstatus, s->intrmask);
+    }
+
+    qemu_set_irq(s->dev.irq[0], (isr != 0));
+}
+
+static void ivshmem_IntrMask_write(IVShmemState *s, uint32_t val)
+{
+    IVSHMEM_DPRINTF("IntrMask write(w) val = 0x%04x\n", val);
+
+    s->intrmask = val;
+
+    ivshmem_update_irq(s, val);
+}
+
+static uint32_t ivshmem_IntrMask_read(IVShmemState *s)
+{
+    uint32_t ret = s->intrmask;
+
+    IVSHMEM_DPRINTF("intrmask read(w) val = 0x%04x\n", ret);
+
+    return ret;
+}
+
+static void ivshmem_IntrStatus_write(IVShmemState *s, uint32_t val)
+{
+    IVSHMEM_DPRINTF("IntrStatus write(w) val = 0x%04x\n", val);
+
+    s->intrstatus = val;
+
+    ivshmem_update_irq(s, val);
+    return;
+}
+
+static uint32_t ivshmem_IntrStatus_read(IVShmemState *s)
+{
+    uint32_t ret = s->intrstatus;
+
+    /* reading ISR clears all interrupts */
+    s->intrstatus = 0;
+
+    ivshmem_update_irq(s, 0);
+
+    return ret;
+}
+
+static void ivshmem_io_writew(void *opaque, uint8_t addr, uint32_t val)
+{
+
+    IVSHMEM_DPRINTF("We shouldn't be writing words\n");
+}
+
+static void ivshmem_io_writel(void *opaque, uint8_t addr, uint32_t val)
+{
+    IVShmemState *s = opaque;
+
+    u_int64_t write_one = 1;
+    u_int16_t dest = val >> 16;
+    u_int16_t vector = val & 0xff;
+
+    addr &= 0xfe;
+
+    switch (addr)
+    {
+        case IntrMask:
+            ivshmem_IntrMask_write(s, val);
+            break;
+
+        case IntrStatus:
+            ivshmem_IntrStatus_write(s, val);
+            break;
+
+        case Doorbell:
+            /* check doorbell range */
+            IVSHMEM_DPRINTF("Writing %ld to VM %d on vector %d\n", write_one, dest, vector);
+            if ((vector > 0) && (vector < s->eventfds_posn_count[dest])) {
+                if (write(s->eventfds[dest][vector], &(write_one), 8) != 8) {
+                    IVSHMEM_DPRINTF("error writing to eventfd\n");
+                }
+            }
+            break;
+        default:
+            IVSHMEM_DPRINTF("Invalid VM Doorbell VM %d\n", dest);
+    }
+}
+
+static void ivshmem_io_writeb(void *opaque, uint8_t addr, uint32_t val)
+{
+    IVSHMEM_DPRINTF("We shouldn't be writing bytes\n");
+}
+
+static uint32_t ivshmem_io_readw(void *opaque, uint8_t addr)
+{
+
+    IVSHMEM_DPRINTF("We shouldn't be reading words\n");
+    return 0;
+}
+
+static uint32_t ivshmem_io_readl(void *opaque, uint8_t addr)
+{
+
+    IVShmemState *s = opaque;
+    uint32_t ret;
+
+    switch (addr)
+    {
+        case IntrMask:
+            ret = ivshmem_IntrMask_read(s);
+            break;
+
+        case IntrStatus:
+            ret = ivshmem_IntrStatus_read(s);
+            break;
+
+        case IVPosition:
+            /* return my id in the ivshmem list */
+            ret = s->vm_id;
+            break;
+
+        default:
+            IVSHMEM_DPRINTF("why are we reading 0x%x\n", addr);
+            ret = 0;
+    }
+
+    return ret;
+
+}
+
+static uint32_t ivshmem_io_readb(void *opaque, uint8_t addr)
+{
+    IVSHMEM_DPRINTF("We shouldn't be reading bytes\n");
+
+    return 0;
+}
+
+static void ivshmem_mmio_writeb(void *opaque,
+                                target_phys_addr_t addr, uint32_t val)
+{
+    ivshmem_io_writeb(opaque, addr & 0xFF, val);
+}
+
+static void ivshmem_mmio_writew(void *opaque,
+                                target_phys_addr_t addr, uint32_t val)
+{
+    ivshmem_io_writew(opaque, addr & 0xFF, val);
+}
+
+static void ivshmem_mmio_writel(void *opaque,
+                                target_phys_addr_t addr, uint32_t val)
+{
+    ivshmem_io_writel(opaque, addr & 0xFF, val);
+}
+
+static uint32_t ivshmem_mmio_readb(void *opaque, target_phys_addr_t addr)
+{
+    return ivshmem_io_readb(opaque, addr & 0xFF);
+}
+
+static uint32_t ivshmem_mmio_readw(void *opaque, target_phys_addr_t addr)
+{
+    uint32_t val = ivshmem_io_readw(opaque, addr & 0xFF);
+    return val;
+}
+
+static uint32_t ivshmem_mmio_readl(void *opaque, target_phys_addr_t addr)
+{
+    uint32_t val = ivshmem_io_readl(opaque, addr & 0xFF);
+    return val;
+}
+
+static CPUReadMemoryFunc *ivshmem_mmio_read[3] = {
+    ivshmem_mmio_readb,
+    ivshmem_mmio_readw,
+    ivshmem_mmio_readl,
+};
+
+static CPUWriteMemoryFunc *ivshmem_mmio_write[3] = {
+    ivshmem_mmio_writeb,
+    ivshmem_mmio_writew,
+    ivshmem_mmio_writel,
+};
+
+static void ivshmem_receive(void *opaque, const uint8_t *buf, int size)
+{
+    IVShmemState *s = opaque;
+
+    ivshmem_IntrStatus_write(s, *buf);
+
+    IVSHMEM_DPRINTF("ivshmem_receive 0x%02x\n", *buf);
+}
+
+static int ivshmem_can_receive(void * opaque)
+{
+    return 8;
+}
+
+static void ivshmem_event(void *opaque, int event)
+{
+//    IVShmemState *s = opaque;
+    IVSHMEM_DPRINTF("ivshmem_event %d\n", event);
+}
+
+static void fake_irqfd(void *opaque, const uint8_t *buf, int size) {
+
+    struct eventfd_entry *entry = opaque;
+    PCIDevice *pdev = entry->pdev;
+
+    IVSHMEM_DPRINTF("fake irqfd on vector %d\n", entry->vector);
+    msix_notify(pdev, entry->vector);
+}
+
+static CharDriverState* create_eventfd_chr_device(void * opaque, int eventfd,
+                                                                    int vector)
+{
+    // create a event character device based on the passed eventfd
+    IVShmemState *s = opaque;
+    CharDriverState * chr;
+
+    chr = qemu_chr_open_eventfd(eventfd);
+
+    if (chr == NULL) {
+        IVSHMEM_DPRINTF("creating eventfd for eventfd %d failed\n", eventfd);
+        exit(-1);
+    }
+
+    if (ivshmem_has_feature(s, IVSHMEM_MSI)) {
+        s->eventfd_table[vector].pdev = &s->dev;
+        s->eventfd_table[vector].vector = vector;
+
+        qemu_chr_add_handlers(chr, ivshmem_can_receive, fake_irqfd,
+                      ivshmem_event, &s->eventfd_table[vector]);
+    } else {
+        qemu_chr_add_handlers(chr, ivshmem_can_receive, ivshmem_receive,
+                      ivshmem_event, s);
+    }
+
+    return chr;
+
+}
+
+static int check_shm_size(IVShmemState *s, int shmemfd) {
+    /* check that the guest isn't going to try and map more memory than the
+     * card server allocated return -1 to indicate error */
+
+    struct stat buf;
+
+    fstat(shmemfd, &buf);
+
+    if (s->ivshmem_size > buf.st_size) {
+        fprintf(stderr, "IVSHMEM ERROR: Requested memory size greater");
+        fprintf(stderr, " than shared object size (%d > %ld)\n",
+                                          s->ivshmem_size, buf.st_size);
+        return -1;
+    } else {
+        return 0;
+    }
+}
+
+static void create_shared_memory_BAR(IVShmemState *s, int fd) {
+
+    s->shm_fd = fd;
+
+    s->ivshmem_offset = qemu_ram_mmap(s->shm_fd, s->ivshmem_size,
+             MAP_SHARED, 0);
+
+    s->ivshmem_ptr = qemu_get_ram_ptr(s->ivshmem_offset);
+
+    /* region for shared memory */
+    pci_register_bar(&s->dev, 2, s->ivshmem_size,
+                       PCI_BASE_ADDRESS_SPACE_MEMORY, ivshmem_map);
+}
+
+static int ivshmem_irqfd(PCIDevice* pdev, uint16_t vector, int fd)
+{
+    struct kvm_irqfd call = { };
+    int r;
+
+    IVSHMEM_DPRINTF("inside irqfd\n");
+    if (vector >= pdev->msix_entries_nr)
+        return -EINVAL;
+    call.fd = fd;
+    call.gsi = pdev->msix_irq_entries[vector].gsi;
+    r = kvm_vm_ioctl(kvm_state, KVM_IRQFD, &call);
+    if (r < 0) {
+        IVSHMEM_DPRINTF("allocating irqfd failed %d\n", r);
+        return r;
+    }
+    return 0;
+}
+
+static int ivshmem_ioeventfd(IVShmemState* s, int posn, int fd, int vector)
+{
+
+    int ret;
+    struct kvm_ioeventfd iofd;
+
+    iofd.datamatch = (posn << 16) | vector;
+    iofd.addr = s->mmio_addr + Doorbell;
+    iofd.len = 4;
+    iofd.flags = KVM_IOEVENTFD_FLAG_DATAMATCH;
+    iofd.fd = fd;
+
+    ret = kvm_vm_ioctl(kvm_state, KVM_IOEVENTFD, &iofd);
+
+    if (ret < 0) {
+        fprintf(stderr, "error assigning ioeventfd (%d)\n", ret);
+        perror(strerror(ret));
+    } else {
+        IVSHMEM_DPRINTF("success assigning ioeventfd (%d:%d)\n", posn, vector);
+    }
+
+    return ret;
+}
+/* notify that a new guest has joined */
+static void new_guest_interrupt(IVShmemState *s)
+{
+    if (msix_enabled(&s->dev)) {
+        msix_notify(&s->dev, 0);
+    } else {
+        ivshmem_IntrStatus_write(s, NEW_GUEST_VAL);
+    }
+}
+
+static void close_guest_eventfds(IVShmemState *s, int posn)
+{
+    int i, guest_curr_max;
+
+    guest_curr_max = s->eventfds_posn_count[posn];
+
+    for (i = 0; i < guest_curr_max; i++)
+        close(s->eventfds[posn][i]);
+
+    free(s->eventfds[posn]);
+    s->eventfds_posn_count[posn] = 0;
+}
+
+static void ivshmem_read(void *opaque, const uint8_t * buf, int flags)
+{
+    IVShmemState *s = opaque;
+    int incoming_fd, tmp_fd;
+    int guest_curr_max;
+    long incoming_posn;
+
+    memcpy(&incoming_posn, buf, sizeof(long));
+    /* pick off s->chr->msgfd and store it, posn should accompany msg */
+    tmp_fd = qemu_chr_get_msgfd(s->chr);
+    IVSHMEM_DPRINTF("posn is %ld, fd is %d\n", incoming_posn, tmp_fd);
+
+    if (tmp_fd == -1) {
+        /* if posn is positive and unseen before then this is our posn*/
+        if ((incoming_posn >= 0) && (s->eventfds[incoming_posn] == NULL)) {
+            /* receive our posn */
+            s->vm_id = incoming_posn;
+            return;
+        } else {
+            /* otherwise an fd == -1 means an existing guest has gone away */
+            IVSHMEM_DPRINTF("posn %ld has gone away\n", incoming_posn);
+            close_guest_eventfds(s, incoming_posn);
+            return;
+        }
+    }
+
+    /* because of the implementation of get_msgfd, we need a dup */
+    incoming_fd = dup(tmp_fd);
+
+    /* if the position is -1, then it's shared memory region fd */
+    if (incoming_posn == -1) {
+
+        s->num_eventfds = 0;
+
+        if (check_shm_size(s, incoming_fd) == -1) {
+            exit(-1);
+        }
+
+        /* creating a BAR in qemu_chr callback may be crazy */
+        create_shared_memory_BAR(s, incoming_fd);
+
+       return;
+    }
+
+    /* each guest has an array of eventfds, and we keep track of how many
+     * guests for each VM */
+    guest_curr_max = s->eventfds_posn_count[incoming_posn];
+    if (guest_curr_max == 0) {
+        s->eventfds[incoming_posn] = (int *) malloc(IVSHMEM_MAX_EVENTFDS *
+                                                                sizeof(int));
+        new_guest_interrupt(s);
+    }
+
+    /* this is an eventfd for a particular guest VM */
+    IVSHMEM_DPRINTF("eventfds[%ld][%d] = %d\n", incoming_posn, guest_curr_max,
+                                                                incoming_fd);
+    s->eventfds[incoming_posn][guest_curr_max] = incoming_fd;
+
+    /* increment count for particular guest */
+    s->eventfds_posn_count[incoming_posn]++;
+
+    /* ioeventfd and irqfd are enabled together,
+     * so the flag IRQFD refers to both */
+    if (ivshmem_has_feature(s, IVSHMEM_IRQFD) && guest_curr_max > 0) {
+        /* allocate ioeventfd for the new fd
+         * received for guest @ incoming_posn */
+        ivshmem_ioeventfd(s, incoming_posn, incoming_fd, guest_curr_max);
+    }
+
+    /* keep track of the maximum VM ID */
+    if (incoming_posn > s->num_eventfds) {
+        s->num_eventfds = incoming_posn;
+    }
+
+    if (incoming_posn == s->vm_id) {
+        if (ivshmem_has_feature(s, IVSHMEM_IRQFD)) {
+            /* setup irqfd for this VM's eventfd */
+            ivshmem_irqfd(&s->dev, guest_curr_max,
+                                s->eventfds[s->vm_id][guest_curr_max]);
+        } else {
+            /* initialize char device for callback
+             * if this is one of my eventfd */
+            s->eventfd_chr[guest_curr_max] = create_eventfd_chr_device(s,
+                s->eventfds[s->vm_id][guest_curr_max], guest_curr_max);
+        }
+    }
+
+    return;
+}
+
+static void ivshmem_reset(DeviceState *d)
+{
+    return;
+}
+
+static void ivshmem_mmio_map(PCIDevice *pci_dev, int region_num,
+                       pcibus_t addr, pcibus_t size, int type)
+{
+    IVShmemState *s = DO_UPCAST(IVShmemState, dev, pci_dev);
+
+    s->mmio_addr = addr;
+    cpu_register_physical_memory(addr + 0, 0x400, s->ivshmem_mmio_io_addr);
+
+    /* now that our mmio region has been allocated, we can receive
+     * the file descriptors */
+    qemu_chr_add_handlers(s->chr, ivshmem_can_receive, ivshmem_read,
+                     ivshmem_event, s);
+
+}
+
+static int pci_ivshmem_init(PCIDevice *dev)
+{
+    IVShmemState *s = DO_UPCAST(IVShmemState, dev, dev);
+    uint8_t *pci_conf;
+    int i;
+
+    /* BARs must be a power of 2 */
+    if (is_power_of_two(s->size))
+        s->ivshmem_size = s->size * 1024* 1024;
+    else {
+        fprintf(stderr, "ivshmem: size must be power of 2\n");
+        exit(1);
+    }
+
+    /* IRQFD requires MSI */
+    if (ivshmem_has_feature(s, IVSHMEM_IRQFD) &&
+        !ivshmem_has_feature(s, IVSHMEM_MSI)) {
+        fprintf(stderr, "ivshmem: ioeventfd/irqfd requires MSI\n");
+        exit(1);
+    }
+
+    pci_conf = s->dev.config;
+    pci_conf[0x00] = 0xf4; // Qumranet vendor ID 0x5002
+    pci_conf[0x01] = 0x1a;
+    pci_conf[0x02] = 0x10;
+    pci_conf[0x03] = 0x11;
+    pci_conf[0x04] = PCI_COMMAND_IOACCESS | PCI_COMMAND_MEMACCESS;
+    pci_conf[0x0a] = 0x00; // RAM controller
+    pci_conf[0x0b] = 0x05;
+    pci_conf[0x0e] = 0x00; // header_type
+
+    s->ivshmem_mmio_io_addr = cpu_register_io_memory(ivshmem_mmio_read,
+                                    ivshmem_mmio_write, s);
+    /* region for registers*/
+    pci_register_bar(&s->dev, 0, 0x400,
+                           PCI_BASE_ADDRESS_SPACE_MEMORY, ivshmem_mmio_map);
+
+    /* allocate the MSI-X vectors */
+    if (ivshmem_has_feature(s, IVSHMEM_MSI)) {
+
+        if (!msix_init(&s->dev, s->vectors, 1, 0)) {
+            pci_register_bar(&s->dev, 1,
+                             msix_bar_size(&s->dev),
+                             PCI_BASE_ADDRESS_SPACE_MEMORY,
+                             msix_mmio_map);
+            IVSHMEM_DPRINTF("msix initialized (%d vectors)\n", s->vectors);
+        } else {
+            IVSHMEM_DPRINTF("msix initialization failed\n");
+        }
+
+        /* 'activate' the vectors */
+        for (i = 0; i < s->vectors; i++) {
+            msix_vector_use(&s->dev, i);
+        }
+    }
+
+    if ((s->chr != NULL) && (strncmp(s->chr->filename, "unix:", 5) == 0)) {
+        /* if we get a UNIX socket as the parameter we will talk
+         * to the ivshmem server later once the MMIO BAR is actually
+         * allocated (see ivshmem_mmio_map) */
+
+        s->eventfds_posn_count = qemu_mallocz(IVSHMEM_MAX_EVENTFDS *
+                                                                sizeof(int));
+
+        IVSHMEM_DPRINTF("using shared memory server (socket = %s)\n",
+                                                            s->chr->filename);
+
+        s->vm_id = -1;
+
+    } else {
+        /* just map the file immediately, we're not using a server */
+        int fd;
+
+        IVSHMEM_DPRINTF("using shm_open (shm object = %s)\n", s->shmobj);
+
+        if ((fd = shm_open(s->shmobj, O_CREAT|O_RDWR,
+                        S_IRWXU|S_IRWXG|S_IRWXO)) < 0) {
+            fprintf(stderr, "kvm_ivshmem: could not open shared file\n");
+            exit(-1);
+        }
+
+        /* mmap onto PCI device's memory */
+        if (ftruncate(fd, s->ivshmem_size) != 0) {
+            fprintf(stderr, "kvm_ivshmem: could not truncate shared file\n");
+        }
+
+        create_shared_memory_BAR(s, fd);
+
+    }
+
+    IVSHMEM_DPRINTF("shared memory size is = %d\n", s->size);
+
+    pci_conf[PCI_INTERRUPT_PIN] = 1; // we are going to support interrupts
+
+    if (!ivshmem_has_feature(s, IVSHMEM_IRQFD)) {
+        s->eventfd_chr = (CharDriverState **)malloc(IVSHMEM_MAX_EVENTFDS *
+                                                            sizeof(void *));
+    }
+
+    return 0;
+}
+
+static int pci_ivshmem_uninit(PCIDevice *dev)
+{
+    IVShmemState *s = DO_UPCAST(IVShmemState, dev, dev);
+
+    cpu_unregister_io_memory(s->ivshmem_mmio_io_addr);
+
+    return 0;
+}
+
+static PCIDeviceInfo ivshmem_info = {
+    .qdev.name  = "ivshmem",
+    .qdev.size  = sizeof(IVShmemState),
+    .qdev.reset = ivshmem_reset,
+    .init       = pci_ivshmem_init,
+    .exit       = pci_ivshmem_uninit,
+    .qdev.props = (Property[]) {
+        DEFINE_PROP_CHR("chardev", IVShmemState, chr),
+        DEFINE_PROP_UINT32("size", IVShmemState, size, 0),
+        DEFINE_PROP_UINT32("vectors", IVShmemState, vectors, 2),
+        DEFINE_PROP_BIT("irqfd", IVShmemState, features, IVSHMEM_IRQFD, false),
+        DEFINE_PROP_BIT("msi", IVShmemState, features, IVSHMEM_MSI, true),
+        DEFINE_PROP_STRING("shm", IVShmemState, shmobj),
+        DEFINE_PROP_END_OF_LIST(),
+    }
+};
+
+static void ivshmem_register_devices(void)
+{
+    pci_qdev_register(&ivshmem_info);
+}
+
+device_init(ivshmem_register_devices)
diff --git a/qemu-char.c b/qemu-char.c
index 048da3f..41cb8c7 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -2076,6 +2076,12 @@  static void tcp_chr_read(void *opaque)
     }
 }
 
+CharDriverState *qemu_chr_open_eventfd(int eventfd){
+
+    return qemu_chr_open_fd(eventfd, eventfd);
+
+}
+
 static void tcp_chr_connect(void *opaque)
 {
     CharDriverState *chr = opaque;
diff --git a/qemu-char.h b/qemu-char.h
index 3a9427b..1571091 100644
--- a/qemu-char.h
+++ b/qemu-char.h
@@ -93,6 +93,9 @@  void qemu_chr_info_print(Monitor *mon, const QObject *ret_data);
 void qemu_chr_info(Monitor *mon, QObject **ret_data);
 CharDriverState *qemu_chr_find(const char *name);
 
+/* add an eventfd to the qemu devices that are polled */
+CharDriverState *qemu_chr_open_eventfd(int eventfd);
+
 extern int term_escape_char;
 
 /* async I/O support */